The present invention is directed generally to medical devices, systems, and methods, particularly for treatment of an eye. In particular, embodiments of the present invention are directed toward contact probes for the delivery of laser energy, and more particularly to contact probes that are used for lowering the intraocular pressure (IOP) in human eyes afflicted with glaucoma. Even more specifically, the present invention is directed toward laser therapy for lowering IOP in glaucomatous eyes via transconjunctival/transcleral ab-externo treatment with infrared laser energy directed to the ciliary body and pigmented ciliary epithelium, pars plicata, and/or the posterior portion of the pars plicata para plana interface.
Glaucoma is a leading cause of blindness. Glaucoma involves the loss of retinal ganglion cells in a characteristic pattern of optic neuropathy. Untreated glaucoma can lead to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness. The loss of visual field due to glaucoma often occurs gradually over a long time and may only be recognized when the loss is already quite advanced. Once lost, this damaged visual field can never be recovered.
Raised intraocular pressure (IOP) is a significant risk factor for developing glaucoma. IOP is a function of production of aqueous humor by the ciliary body of the eye and its drainage through the trabecular meshwork and all other outflow pathways including the uveoscleral pathway. Aqueous humor is a complex mixture of electrolytes, organics solutes, and other proteins that supply nutrients to the non-vascularized tissues of the anterior chamber of the eye. It flows from the ciliary bodies into the posterior chamber of the anterior segment, bounded posteriorly by the lens and the ciliary zonule and bounded anteriorly by the iris. Aqueous humor then flows through the pupil of the iris into the anterior chamber, bounded posteriorly by the iris and anteriorly by the cornea. In the conventional aqueous humor outflow path, the trabecular meshwork drains aqueous humor from the anterior chamber through the trabecular meshwork exiting into the Schlemm's canal into scleral plexuses and the general venous blood circulation. In open angle glaucoma there is reduced flow through the trabecular meshwork. In angle closure glaucoma, the iris is pushed forward against the trabeular meshwork, blocking fluid from escaping.
Uveoscleral outflow is an accessory outflow and accounts from 10-20% of total aqueous humor outflow. Enhancing uveocleral outflow is assuming a growing importance in the management of glaucoma. In uveoscleral outflow, aqueous humor enters the ciliary muscles from the anterior chamber and exits through the supraciliary space and across the anterior or posterior sclera. Uveoscleral outflow contributes significantly to total aqueous humor outflow with a reduction in intraocular pressure.
Currently, glaucoma therapies aim to reduce IOP by either limiting the production of aqueous humor or by increasing the outflow of aqueous humor. Medications such as beta-blockers, carbonic anhydrase inhibitors, etc., are used as the primary treatment to reduce the production of aqueous humor. Medications may also be used as the primary therapy to increase the outflow of the aqueous humor. Miotic and cholinergic drugs increase the trabecular outflow, while prostaglandin drugs, for example, Latanoprost and Bimatoprost, increase the uveoscleral outflow. These drugs, however, are expensive and may have undesirable side effects, which can cause compliance-dependent problems over time especially when more than one drug is prescribed.
Surgery may also be used to increase the outflow or to lower the production of aqueous humor. Laser trabeculoplasty is the application of a laser beam over areas of the trabecular meshwork to increase the outflow. Cyclocryotherapy and laser cyclophotocoagulation are surgical interventions over the ciliary processes to lower the production of aqueous humor. Although they may be effective, these destructive surgical interventions are normally used as a last resource in the management of glaucoma due to the risk of the severe complication of phthisis bulbi. Other adverse side effects of cyclodestructive surgical procedures may include temporary or permanent mydriasis (pupil dilation), ocular hypotony, inflammation of the anterior eye segment, which may be associated with an increased incidence of macula complications, and loss of best corrected visual acuity. Still other adverse side effects include transient hyphaema and exudates in the anterior chamber, uveitis, and necrotizing scleritis.
In laser transscleral cyclophotocoagulation, a continuous wave (CW) of high intensity infrared laser energy is directed toward selected portions of the pars plicata region of the ciliary body, structures under the scleral layers and the overlying conjunctiva. Selected portions of the ciliary body and related processes are permanently destroyed, thereby decreasing the overall production of aqueous humor. Laser energy may be directed through air to a patient seated at a special slit lamp. Alternatively, laser energy may be delivered through the use of fiber optic hand pieces placed in contact with the patient's eyeball. In both laser energy delivery methods, however, accurately and repeatedly directing a laser beam a subsurface non-visible target such as the ciliary body can be challenging for a surgeon. Thus, contact hand piece probes (for example, the G-Probe available through IRIDEX Corporation of Mountain View, Calif. and described in U.S. Pat. No. 5,272,595, the full disclosure of which is incorporated herein by reference in its entirety) have been designed to facilitate the aiming of a laser toward the pars plicata region of the ciliary body. The G-Probe, for example, has special contours that facilitate consistent placement and aiming of the probe relative to external landmark structures of the eye (e.g. limbus), thereby guiding the laser light energy to the correct target tissue, thus likely decreasing the likelihood of adverse events and increasing the likelihood of favorable clinical responses.